It is known to produce a warp-knit support tape to which is stitched a helicoidal monofilamentary coupling element. The slide-fastener stringer half constituted by the coupling element, tape, and stitching securing the two together is ideally suited for use in a light-duty or medium-duty slide fastener.
For heavy-duty slide fasteners a helicoidal monofilamentary coupling element is not generally used. Instead a succession of discrete teeth of metal or of synthetic-resin material are secured to the edge of the support tape. To this end the support-tape edge must be thickened so that the teeth can be mounted astraddle the edge. In most arrangements this is done simply by loading the edgemost needle of the warp-knitting machine with a warp end of the largest possible gauge that the needle can accommodate.
Practice has shown, however, that such a warp-knit tape is often insufficiently strong at its edge to withstand the considerable transverse forces that are applied to it. In addition such a tape frequently has at least limited longitudinal stretchability at the edge which the teeth straddle, so that the intertooth spacing can change as the tape is deformed, which renders the slide fastener almost worthless in uses where longitudinal stress is present.